Study on the Inhibition Mechanism of Corrosion under Inert Deposit-Covered X65 Steel by Three Corrosion Inhibitors

In order to solve the problem of under-deposit corrosion caused by typical inert minerals in oil and gas fields, three corrosion inhibitors with small molecular weight thiourea (TU), oil-soluble alkyl imidazoline (IM) and water-soluble thiourea imidazoline (TAI) were selected. The corrosion inhibition effect and mechanism of the them under SiO2 and CaCO3 deposit were studied by surface analysis, electrochemical analysis and theoretical calculations. The results show that TU, IM and TAI can adsorb on the metal surface through the deposits, and the corrosion inhibition efficiency is η(TAI) > η(TU) > η(IM). TU and TAI are mixed corrosion inhibitors that inhibit both the cathode and the anode reactions, and the thiourea group in TU and TAI can form coordination chemical bonds with the empty d orbital of iron atoms as electron-rich regions. Due to hydrophobic groups, the adsorption film formed by TAI on the metal surface is denser. However, it is difficult for IM to form a continuous protective corrosion inhibitor film under the two deposits, so it shows poor corrosion inhibition performance.